AQA A LEVEL BIOLOGY PAPER 3 2020 MARK SCHEME

Question Marking Guidance Mark Comments

01.1

1. Laboratory-raised female (guppies) might not

react/behave/choose in the same way (as wild

guppies);

2. (Transparent) barrier might not allow for normal

(courtship) behaviour/interaction;

3. Do not know if (guppies) have been used in

previous experiments;

4. 10 minutes might not be long enough for females

to make a (final) choice

OR

Not enough time for females to make a (final)

choice;

3 max

Ignore answers

relating to sample size

1. Accept laboratoryraised female

(guppies) might

not be

representative of

wild females

2. Accept choice

might involve

chemical/

mechanical

signals/interaction

2. Accept colour

might not be the

only thing females

are attracted to

4. Accept

descriptions of a

choice eg ‘show

attraction’

01.2

1. (Females with large brains) will mate with males

bright in colour;

2. Their (male) offspring would be (more likely to

be) bright in colour;

3. (Bright in colour male) offspring could attract

larger brained females;

4. The population/offspring could (evolve to) have

larger brains;

5. The population/offspring are better at

identifying/avoiding predators;

3 max

Accept answers that

include references to

alleles

4. and 5. Ignore

answers relating to

females only

MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2020

7

01.3

1. Not geographically isolated;

2. (Leading to) reproductive isolation

OR

Gene pools kept separate;

3. Changes in allele frequencies;

4. Cannot breed/mate to produce fertile offspring;

3 max

1. Accept are in the

same area

2. Accept large

brained females will

only mate with

males bright in

colour and small

brained females will

only mate with

males dull in colour

3. Reject gene

frequencies

4. Reject inbreeding

MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2020

8

Question Marking Guidance Mark Comments

02.1 Interspecific (competition); 1

02.2

1. Do not provide the livestock/cows/horses/yaks

with extra food, as their populations will not grow

large enough to cause competition

OR

Keep small numbers of livestock/cow/horse/yak,

so their populations will not grow large enough to

cause competition;

2. Do not farm horse/choose animals other than

horse to farm, as they have the same habitat

and (very) similar food to the ibex;

3. Keep horses (but) in enclosed/separate areas,

as they occupy the same habitats as ibex;

4. Farm cows, as they have the least similar food

and (one of the least similar) habitat (to that of

the ibex);

5. Farm yaks, as despite eating the same food,

they live in a very different habitat;

6. (Only) grow crops, so no competition;

3 max

Requires suggestion

and explanation for

each mark

2. Accept farm fewer

horses as they

have the same

habitat and (very)

similar food to the

ibex

3. Accept

descriptions

of enclosed areas,

eg fenced areas or

accept do not let

horses out

6. Accept examples

of crops

MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2020

9

Question Marking Guidance Mark Comments

03.1

1. Mutation in the viral DNA/RNA/genome/genetic

material;

2. Altered (tertiary structure of the) viral

attachment protein;

3. Allows it/attachment protein/virus to bind (to

receptors of other species);

2 max 1. Accept named

examples

mutations

2. Accept ‘antigen’

for ‘attachment

protein’

2. Accept causes

antigenic variability

3. Accept descriptions

of binding eg is

complementary

03.2

For one mark, accept any two of the following:

• The polymerase chain reaction

• Genetic/DNA fingerprinting

• (Gel) electrophoresis

• DNA/genome sequencing;

1

Accept PCR for

polymerase chain

reaction

Accept

autoradiography

Accept DNA

hybridisation

Accept compare

DNA/base sequence

for ‘DNA sequencing’

Ignore compare mRNA

base sequence

Ignore compare amino

acid sequence

Ignore DNA probes

03.3

1. (The scientists) could identify proteins (that

derive from the genetic code)

OR

(The scientists) could identify the proteome;

2. (They) could (then) identify potential antigens

(to use in the vaccine);

2

2. Reject if answer

suggests vaccine

contains antibodies